Illumination structure including cavity and TIR structure

Abstract

A thin plastic light guide is formed to have cavities on one surface and TIR (total internal reflection) structures directly above the cavities. LEDs mounted on a printed circuit board are positioned hi the cavities. The cavity walls are shaped to refract the LED light and direct the LED light toward the TIR structures to most efficiently make use of the TIR structures. The TIR structures may have a cusp or cone shape. The top ceiling of the cavities may be shaped to direct light at the TIR structure so as to leak through the TIR structure and blend the light with light leaking through surrounding portions of the light guide. The LEDs may be distributed only near the edges of the light guide or over the entire back surface of the light guide. A diffuser sheet may be laminated over the light guide to further mix the light.

What is being claimed is: 
     
       1. An illumination structure, comprising:
 a light guide configured to receive light emitted in an angular distribution that is substantially centered around a central axis and guide the received light between a first surface of the light guide and an opposing second surface of the light guide, 
 the first surface including a cavity formed in the first surface, the cavity having a convex central portion that is substantially centered around the central axis, the convex central portion configured to refract at least some of the emitted light into the light guide as refracted light, 
 the convex central portion being closer to the first surface at a center of the convex central portion than at an edge of the convex central portion, 
 the convex central portion having a cross-section, taken in a plane that includes the central axis, that lacks a corner at the central axis, 
 the second surface including a total internal reflection (TIR) structure that is shaped to reflect at least some of the refracted light via TIR and propagate the reflected light in the light guide generally away from the central axis, 
 the TIR structure having a cross-section, taken in the plane that includes the central axis, that includes a corner at the central axis and convex cross-sectional portions on opposite sides of the corner. 
 
     
     
       2. The illumination structure of  claim 1 , wherein:
 the first surface extends substantially in a first plane; and 
 the second surface extends substantially in a second plane. 
 
     
     
       3. The illumination structure of  claim 2 , wherein the first plane and the second plane are generally orthogonal to the central axis. 
     
     
       4. The illumination structure of  claim 3 , wherein the cavity and the TIR structure extend into the light guide such that the light guide is fully located between the first plane and the second plane. 
     
     
       5. The illumination structure of  claim 2 , further comprising a light-emitting diode configured to emit the light in the angular distribution that is substantially centered around the central axis, the light-emitting diode being at least partially located in the cavity between the first plane and the second plane. 
     
     
       6. The illumination structure of  claim 1 , wherein the convex central portion is generally orthogonal to the central axis at a center of the convex central portion. 
     
     
       7. The illumination structure of  claim 1 , wherein the convex central portion adjoins a side wall of the cavity at a corner that encircles the convex central portion. 
     
     
       8. The illumination structure of  claim 1 , wherein the TIR structure is shaped as a portion of a cone. 
     
     
       9. The illumination structure of  claim 1 , wherein the light guide has light extraction features formed on the second surface. 
     
     
       10. The illumination structure of  claim 1 , further comprising a diffusing sheet overlying the second surface of the light guide. 
     
     
       11. The illumination structure of  claim 1 , wherein the light guide has light extraction features formed on the first surface. 
     
     
       12. A method of producing illumination, the method comprising:
 receiving, with a light guide, emitted light having an angular distribution that is substantially centered around a central axis; and 
 guiding the received light between a first surface of the light guide and an opposing second surface of the light guide, the first surface including a cavity formed in the first surface, the cavity having a convex central portion that is substantially centered around the central axis, the convex central portion being closer to the first surface at a center of the convex central portion than at an edge of the convex central portion, the convex central portion having a cross-section, taken in a plane that includes the central axis, that lacks a corner at the central axis, the second surface including a total internal reflection (TIR) structure, the TIR structure having a cross-section, taken in the plane that includes the central axis, that includes a corner at the central axis and convex cross-sectional portions on opposite sides of the corner; 
 refracting, with the convex central portion, at least some of the emitted light into the light guide as refracted light; and 
 reflecting, via TIR from the TIR structure, at least some of the refracted light to propagate in the light guide generally away from the central axis. 
 
     
     
       13. The method of  claim 12 , wherein:
 the first surface extends substantially in a first plane; 
 the second surface extends substantially in a second plane; 
 the first plane and the second plane are generally orthogonal to the central axis; 
 the cavity and the TIR structure extend into the light guide such that the light guide is fully located between the first plane and the second plane; 
 a light-emitting diode is at least partially located in the cavity between the first plane and the second plane; 
 the convex central portion is generally orthogonal to the central axis at a center of the convex central portion; and 
 the convex central portion adjoins a side wall of the cavity at a corner that encircles the convex central portion. 
 
     
     
       14. The method of  claim 12 , further comprising emitting the emitted light from a light-emitting diode. 
     
     
       15. An illumination structure, comprising:
 a light guide configured to receive light emitted in an angular distribution that is substantially centered around a central axis and guide the received light between a first surface of the light guide and an opposing second surface of the light guide, 
 the first surface including a cavity formed in the first surface, the cavity having a convex central portion that is substantially centered around the central axis and is generally orthogonal to the central axis at a center of the convex central portion, the convex central portion adjoining a side wall of the cavity at a corner that encircles the convex central portion, the convex central portion configured to refract at least some of the emitted light into the light guide as refracted light, the convex central portion being closer to the first surface at a center of the convex central portion than at an edge of the convex central portion, the convex central portion having a cross-section, taken in a plane that includes the central axis, that lacks a corner at the central axis, 
 the second surface including a total internal reflection (TIR) structure that is shaped to reflect at least some of the refracted light via TIR to propagate in the light guide generally away from the central axis, 
 a cross-section of the TIR structure, taken in a plane that includes the central axis, including a corner at the central axis and convex cross-sectional portions on opposite sides of the corner; and 
 a diffusing sheet overlying the second surface. 
 
     
     
       16. The illumination structure of  claim 15 , wherein:
 the first surface extends substantially in a first plane; 
 the second surface extends substantially in a second plane; and 
 the first plane and the second plane are generally orthogonal to the central axis. 
 
     
     
       17. The illumination structure of  claim 16 , wherein the cavity and the TIR structure extend into the light guide such that the light guide is fully located between the first plane and the second plane. 
     
     
       18. The illumination structure of  claim 16 , further comprising a light-emitting diode configured to emit the light in the angular distribution that is substantially centered around the central axis, the light-emitting diode being at least partially located in the cavity between the first plane and the second plane. 
     
     
       19. The illumination structure of  claim 15 , wherein the TIR structure is shaped as a portion of a cone.